Semiconductor devices are used in a variety of electronic applications, such as computers, cellular phones, personal computing devices, and many other applications. Home, industrial, and automotive devices that in the past comprised only mechanical components now have electronic parts that require semiconductor devices, for example.
Semiconductor devices are manufactured by depositing many different types of material layers over a semiconductor workpiece or wafer, and patterning the various material layers using lithography. The material layers typically comprise thin films of conductive, semiconductive, and insulating materials that are patterned and etched to form integrated circuits (IC's). There may be a plurality of transistors, memory devices, switches, conductive lines, diodes, capacitors, logic circuits, and other electronic components formed on a single die or chip.
In the past, aluminum was typically used as a conductive line material in integrated circuits. Silicon dioxide was typically used as the insulating material between aluminum conductive lines. However, as semiconductor devices are scaled down in size, there is a trend towards the use of copper for interconnect material, in conjunction with the use of low dielectric constant (k) materials. Advantages of using copper for interconnects in integrated circuits include decreased resistivity, resulting in increased speed, decreased RC time delay, and the ability to form thinner conductive lines. Copper has increased electromigration resistance, so that higher current densities may be used.
However, there are some challenges in working with copper in a manufacturing process. While aluminum may be subtractively etched, copper is difficult to subtractively etch, and thus, damascene processes are typically used to form copper conductive features. In a damascene process, a dielectric material is deposited over a wafer, and then the dielectric material is patterned with a conductive feature pattern. The conductive feature pattern typically comprises a plurality of trenches, for example. The trenches are then filled in with conductive material, and a chemical-mechanical polish (CMP) process is used to remove the excess conductive material from the top surface of the dielectric material. The conductive material remaining within the dielectric material comprises conductive features such as conductive lines or vias, as example.
Copper has a tendency to diffuse into adjacent material layers, such as the insulating layers the copper interconnects are formed in. Thus, diffusion barriers are used to prevent the diffusion of copper. Typical diffusion barrier materials are Ta and TaN, as examples. Because these materials have a higher resistance than copper, the diffusion barriers are typically made very thin to avoid excessively increasing the resistance of conductive features. These thin prior art diffusion barriers have a tendency towards the formation of weak spots and holes, which can permit copper to diffuse into adjacent material layers.
Thus, what are needed in the art are improved diffusion barrier layers and methods of formation thereof.